Fuel cell

ABSTRACT

A fuel cell includes a membrane electrode assembly, a first metal separator, a second metal separator, linear protrusions, and embossed protrusions. The first metal separator is stacked on the membrane electrode assembly. The second metal separator is stacked on the first metal separator to define a coolant channel between the metal separators. The first metal separator includes wave-shaped protrusions projecting from the first metal separator by a first height to define to form the coolant channel. The linear protrusions are connected to both distal ends of each of the wave-shaped protrusions. The linear protrusions project from the first metal separator by a second height smaller than the first height. The embossed protrusions are connected to tip ends of the linear protrusions. The embossed protrusions project from the first metal separator by a third height larger than the second height to be in contact with the second metal separator.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 toJapanese Patent Application No. 2015-208404, filed Oct. 22, 2015,entitled “Fuel Cell.” The contents of this application are incorporatedherein by reference in their entirety.

BACKGROUND

1. Field

The present disclosure relates to a fuel cell.

2. Description of the Related Art

In general, a solid polymer electrolyte fuel cell includes a solidpolymer electrolyte membrane, which is a polymer ion-exchange membrane.The fuel cell includes a membrane electrode assembly (MEA), in which ananode electrode is disposed on one surface of the solid polymerelectrolyte membrane and a cathode electrode is disposed on the othersurface of the solid polymer electrolyte membrane. The anode electrodeand the cathode electrode each include a catalyst layer (electrodecatalyst layer) and a gas diffusion layer (porous carbon).

The membrane electrode assembly and separators (bipolar plates) thatsandwich the membrane electrode assembly constitute a power generationcell (unit fuel cell). A predetermined number of power generation cellsare stacked and used, for example, as a vehicle fuel cell stack.

In some fuel cells, metal separators having thin plate-like shapes areused. On a surface of one of the metal separators facing the anodeelectrode, a plurality of wave-shaped fuel gas channels (reactant gaschannels), which are wave-shaped in plan view, are formed. A fuel gasflows through the fuel gas channels along an electrode surface of theanode electrode. On a surface of one of the metal separators facing thecathode electrode, a plurality of wave-shaped oxidant gas channels(reactant gas channels), which are wave-shaped in plan view, are formed.An oxidant gas flows through the oxidant gas channels along an electrodesurface of the cathode electrode.

A coolant channel is formed between the back side of the wave-shapedfuel gas channels of one of the separators and the back side of thewave-shaped oxidant gas channels of an adjacent separator. A coolantflows through the coolant channel in a direction along the electrodesurfaces.

When the fuel cell is a so-called “internal-manifold fuel cell”, areactant gas manifold, through which a reactant gas flows, and a coolantmanifold, through which a coolant flows, are formed so as to extendthrough the power generation cell in the stacking direction. In thiscase, because the reactant gas manifold has a comparatively smallopening area, in order to uniformly and reliably supply the reactant gasto an electrode reaction surface, a buffer portion, which includes aplurality of embossed portion or guide portions, is formed between thereactant gas manifold and the reactant gas channel. For example,Japanese Unexamined Patent Application Publication No. 2014-137937describes a fuel cell stack utilizing such technology.

SUMMARY

According to one aspect of the present invention, a fuel cell includes amembrane electrode assembly and metal separators. In the membraneelectrode assembly, electrodes are disposed on both sides of anelectrolyte membrane. The metal separators are stacked on the membraneelectrode assembly. A coolant channel is formed between a first metalseparator and a second metal separator that are adjacent to each other.The coolant channel allows a coolant to flow in a direction along anelectrode surface. The first metal separator includes wave-shapedprotrusions, linear protrusions, and embossed protrusions. Between eachpair of the wave-shaped protrusions, a wave-shaped channel groove isformed. Each of the wave-shaped protrusions has a wave shape in planview. The wave-shaped channel groove is included in the coolant channel.The linear protrusions are connected to both ends of each of thewave-shaped protrusions. Each of the linear protrusions has a heightsmaller than that of each of the wave-shaped protrusions. Each of theembossed protrusions is connected to an end portion of a correspondingone of the linear protrusions. Each of the embossed protrusions has aheight larger than that of each of the linear protrusions and is incontact with the second metal separator.

According to another of the present invention, a fuel cell includes amembrane electrode assembly, a first metal separator, a second metalseparator, first and second linear protrusions, and first and secondembossed protrusions. The membrane electrode assembly has a first endand second end opposite to the first end in an extending direction. Themembrane electrode assembly includes an electrolyte membrane and firstand second electrodes sandwiching the electrolyte membrane therebetweenin a stacking direction substantially perpendicular to the extendingdirection. The first metal separator is stacked on the membraneelectrode assembly in the stacking direction. The second metal separatoris stacked on the first metal separator in the stacking direction todefine a coolant channel between the first metal separator and thesecond metal separator. The coolant channel extends in the extendingdirection. The first metal separator includes wave-shaped protrusionseach of which has a wave shape viewed in the stacking direction andprojects from the first metal separator toward the second metalseparator by a first height in the stacking direction to define awave-shaped channel groove between the wave-shaped protrusions to formthe coolant channel. Each of the wave-shaped protrusions has a firstdistal end and the second distal end opposite to the first distal end inthe extending direction. The first and second linear protrusions areconnected to the first distal end and the second distal end of each ofthe wave-shaped protrusions, respectively. Each of the first and secondlinear protrusions has a straight shape extending in the extendingdirection and projects from the first metal separator toward the secondmetal separator by a second height in the stacking direction. The secondheight is smaller than the first height. The first and second embossedprotrusions are connected to a first tip end of the first linearprotrusion and the second tip end of the second linear protrusion,respectively. The first and second embossed protrusions projects fromthe first metal separator toward the second metal separator by a thirdheight in the stacking direction to be in contact with the second metalseparator. The third height is larger than the second height.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings.

FIG. 1 is an exploded perspective view of a power generation cellincluded in a fuel cell according to an embodiment of the presentdisclosure.

FIG. 2 is a sectional view of the power generation cell taken along lineII-II of FIG. 1.

FIG. 3 is a plan view of a first metal separator of the power generationcell.

FIG. 4 is a plan view of a second metal separator of the powergeneration cell.

FIG. 5 is a plan view of a third metal separator of the power generationcell.

FIG. 6 is a plan view of a first membrane electrode assembly of thepower generation cell.

FIG. 7 is a plan view of a second membrane electrode assembly of thepower generation cell.

DESCRIPTION OF THE EMBODIMENTS

The embodiment(s) will now be described with reference to theaccompanying drawings, wherein like reference numerals designatecorresponding or identical elements throughout the various drawings.

Referring to FIGS. 1 and 2, a fuel cell 10 according to an embodiment ofthe present disclosure includes a plurality of power generation cells 12that are stacked in a horizontal direction (direction of arrow A) or ina vertical direction (direction of arrow C). The fuel cell 10 is used,for example, as a vehicle fuel cell stack mounted in a fuel cellelectric automobile (not shown).

Each of the power generation cells 12 includes a first metal separator14, a first membrane electrode assembly 16 a, a second metal separator18, a second membrane electrode assembly 16 b, and a third metalseparator 20.

Each of the first metal separator 14, the second metal separator 18, andthe third metal separator 20 is made from, for example, a steel plate, astainless steel plate, an aluminum plate, a galvanized steel plate, orthe like. Each of the first metal separator 14, the second metalseparator 18, and the third metal separator 20, which has a rectangularshape in plan view, is made by press-forming a thin metal plate so as tohave a wave-shaped cross section.

Referring to FIG. 1, an oxidant gas inlet manifold 22 a and a fuel gasoutlet manifold 24 b are disposed in the power generation cell 12 so asto extend in the direction of arrow A through one end portion of thepower generation cell 12 in the longitudinal direction (direction ofarrow B). An oxidant gas, such as an oxygen-containing gas, is suppliedthrough the oxidant gas inlet manifold 22 a. A fuel gas, such as ahydrogen-containing gas, is discharged through the fuel gas outletmanifold 24 b.

A fuel gas inlet manifold 24 a and an oxidant gas outlet manifold 22 bare disposed in the power generation cell 12 so as to extend in thedirection of arrow A through the other end portion of the powergeneration cell 12 in the longitudinal direction. The fuel gas issupplied through the fuel gas inlet manifold 24 a. The oxidant gas isdischarged through the oxidant gas outlet manifold 22 b.

A pair of coolant inlet manifolds 25 a are disposed in the powergeneration cell 12 so as to extend in the direction arrow A throughupper and lower end portions (that are near the oxidant gas inletmanifold 22 a) of the power generation cell 12 in the transversaldirection (direction of arrow C). A coolant is supplied through thecoolant inlet manifolds 25 a. A pair of coolant outlet manifolds 25 bare disposed in upper and lower end portions (that are near the fuel gasinlet manifold 24 a) of the power generation cell 12 in the transversaldirection. The coolant is discharged through the coolant outletmanifolds 25 b.

Referring to FIG. 3, a first oxidant gas channel 26, which is connectedto the oxidant gas inlet manifold 22 a and the oxidant gas outletmanifold 22 b, is formed on a surface 14 a of the first metal separator14 (corresponding to “a second one of the metal separators” in theclaims) facing the first membrane electrode assembly 16 a. The back sideof the first oxidant gas channel 26 forms a part of a coolant channel27.

The first oxidant gas channel 26 includes wave-shaped channel grooves 26a, which are formed between a plurality of wave-shaped protrusions 26 textending in the direction of arrow B. Each of the wave-shapedprotrusions 26 t has a wave shape in plan view, and each of thewave-shaped channel grooves 26 a has a wave shape in plan view. Each ofthe wave-shaped channel grooves 26 a may have a curved wave shape, whichis made up of curved segments, or may have a zigzag shape, which is madeup of linear segments. Other wave-shaped protrusions described below arestructured in the same way as the wave-shaped protrusions 26 t. An inletlinear protrusion 28 ta and an outlet linear protrusion 28 tb arerespectively connected to an inlet end portion and an outlet end portionof each of the wave-shaped protrusions 26 t.

Referring to FIG. 2, the height t2 of the inlet linear protrusion 28 tafrom a flat surface 26 f is smaller than the height t1 of thewave-shaped protrusion 26 t from the flat surface 26 f (t1>t2). Theoutlet linear protrusion 28 tb is structured in the same way as theinlet linear protrusion 28 ta.

Because the height of each of the inlet linear protrusions 28 ta and theoutlet linear protrusions 28 tb is smaller than that of each of thewave-shaped protrusions 26 t, the depths of channels formed between theinlet linear protrusions 28 ta and the outlet linear protrusions 28 tbare smaller than the depths of the wave-shaped channel grooves 26 a.Therefore, pressure drop in the channels between the inlet linearprotrusions 28 ta and between the outlet linear protrusions 28 tb islarge, and high drainage performance is obtained. As described below,each the first metal separator 14, the second metal separator 18, andthe third metal separator 20 includes inlet linear protrusions andoutlet linear protrusions, each having a height smaller than that ofeach of the wave-shaped protrusions, so that the flow conditions and thelike of the reactant gases can be made uniform.

Referring to FIG. 3, a first oxidant gas inlet buffer portion 30 a isdisposed outward from the inlet linear protrusions 28 ta, and a firstoxidant gas outlet buffer portion 30 b is disposed outward from theoutlet linear protrusions 28 tb. A plurality of embossed protrusions 30ae (the other embossed protrusions) are formed in the first oxidant gasinlet buffer portion 30 a so as to protrude beyond a surface 14 b(toward the coolant channel 27). A plurality of embossed protrusions 30be (the other embossed protrusions) are formed in the first oxidant gasoutlet buffer portion 30 b so as to protrude beyond the surface 14 b(toward the coolant channel 27). The embossed protrusions 30 ae and 30be each may have a circular shape, an elliptical shape, or a polygonalshape, such as a quadrangular shape.

A plurality of inlet connection grooves 31 a are formed between thefirst oxidant gas inlet buffer portion 30 a and the oxidant gas inletmanifold 22 a. A plurality of outlet connection grooves 31 b are formedbetween the first oxidant gas outlet buffer portion 30 b and the oxidantgas outlet manifold 22 b.

Referring to FIG. 1, a first fuel gas channel 34, which is connected tothe fuel gas inlet manifold 24 a and the fuel gas outlet manifold 24 b,is formed on a surface 18 a of the second metal separator 18 facing thefirst membrane electrode assembly 16 a. The first fuel gas channel 34includes wave-shaped channel grooves 34 a, which are formed between aplurality of wave-shaped protrusions 34 t extending in the direction ofarrow B. An inlet linear protrusion 36 ta and an outlet linearprotrusion 36 tb are respectively connected to an inlet end portion andan outlet end portion of each of the wave-shaped protrusion 34 t.

A first fuel gas inlet buffer portion 37 a is disposed outward from theinlet linear protrusions 36 ta, and a first fuel gas outlet bufferportion 37 b is disposed outward from the outlet linear protrusions 36tb.

A plurality of inlet connection grooves 35 a are formed between thefirst fuel gas inlet buffer portion 37 a and the fuel gas inlet manifold24 a. The inlet connection grooves 35 a are covered by a cover member 39a. A plurality of outlet connection grooves 35 b are formed between thefirst fuel gas outlet buffer portion 37 b and the fuel gas outletmanifold 24 b. The outlet connection grooves 35 b are covered by a covermember 39 b.

Referring to FIG. 4, a second oxidant gas channel 38, which is connectedto the oxidant gas inlet manifold 22 a and the oxidant gas outletmanifold 22 b, is formed on a surface 18 b of the second metal separator18 facing the second membrane electrode assembly 16 b. The secondoxidant gas channel 38 includes wave-shaped channel grooves 38 a (orlinear channel grooves), which are formed between a plurality ofwave-shaped protrusions 38 t extending in the direction of arrow B. Theshape of the back side of the second oxidant gas channel 38, which isformed on the second metal separator 18, is the shape of the first fuelgas channel 34.

An inlet linear protrusion 40 ta and an outlet linear protrusion 40 tbare respectively connected to an inlet end portion and an outlet endportion of each of the wave-shaped protrusions 38 t. Referring to FIG.2, the height t4 of the inlet linear protrusion 40 ta from a flatsurface 38 f is smaller than the height t3 of the inlet linearprotrusion 40 ta from the flat surface 38 f (t3>t4). The outlet linearprotrusion 40 tb is structured in the same way as the inlet linearprotrusion 40 ta.

Referring to FIG. 4, a second oxidant gas inlet buffer portion 42 a isdisposed outward from the inlet linear protrusions 40 ta, and a secondoxidant gas outlet buffer portion 42 b is disposed outward from theoutlet linear protrusions 40 tb. A plurality of inlet connection grooves46 a are formed between the second oxidant gas inlet buffer portion 42 aand the oxidant gas inlet manifold 22 a. A plurality of outletconnection grooves 46 b are formed between the second oxidant gas outletbuffer portion 42 b and the oxidant gas outlet manifold 22 b.

Referring to FIG. 1, a second fuel gas channel 48, which is connected tothe fuel gas inlet manifold 24 a and the fuel gas outlet manifold 24 b,is formed on a surface 20 a of the third metal separator 20(corresponding to “a first one of the metal separators” in the claims)facing the second membrane electrode assembly 16 b. The second fuel gaschannel 48 includes wave-shaped channel grooves 48 a, which are formedbetween a plurality of wave-shaped protrusions 48 t extending in thedirection of arrow B. An inlet linear protrusion 50 ta and an outletlinear protrusion 50 tb are respectively connected to an inlet endportion and an outlet end portion of each of the wave-shaped protrusions48 t.

A second fuel gas inlet buffer portion 53 a is disposed at a positionoutward from the inlet linear protrusions 50 ta and near the fuel gasinlet manifold 24 a. A second fuel gas outlet buffer portion 53 b isdisposed at a position outward from the outlet linear protrusion 50 tband near the fuel gas outlet manifold 24 b.

A plurality of inlet connection grooves 54 a are formed between thesecond fuel gas inlet buffer portion 53 a and the fuel gas inletmanifold 24 a. The inlet connection grooves 54 a are covered by a covermember 56 a. A plurality of outlet connection grooves 54 b are formedbetween the second fuel gas outlet buffer portion 53 b and the fuel gasoutlet manifold 24 b. The outlet connection grooves 54 b are covered bya cover member 56 b.

Referring to FIG. 5, on a surface 20 b of the third metal separator 20,a part of the coolant channel 27 is formed on the back side of thesecond fuel gas channel 48. The coolant channel 27 includes wave-shapedchannel grooves 27 a, which are formed between a plurality ofwave-shaped protrusions 27 t extending in the direction of arrow B. Aninlet linear protrusion 51 ta and an outlet linear protrusion 51 tb arerespectively connected to an inlet end portion and an outlet end portionof each of the wave-shaped protrusion 27 t.

An embossed protrusion 52 ta, which protrudes from the second fuel gaschannel 48 toward the coolant channel 27, is integrally formed with anend portion of each of the inlet linear protrusions 51 ta. An embossedprotrusion 52 tb, which protrudes from the second fuel gas channel 48toward the coolant channel 27, is integrally formed with an end portionof each of the outlet linear protrusions 51 tb.

Referring to FIG. 2, the height t6 of the inlet linear protrusion 51 tafrom a flat surface 27 f is smaller than the height t5 of thewave-shaped protrusion 27 t from the flat surface 27 f (t5>t6). Theoutlet linear protrusion 51 tb is structured in the same way as theinlet linear protrusion 51 ta.

The height t7 of the embossed protrusion 52 ta from the flat surface 27f is larger than the height t6 of the inlet linear protrusion 51 ta fromthe flat surface 27 f (t7>t6). As long the embossed protrusion 52 ta isin contact with the surface 14 b of the first metal separator 14, theheight t7 may be the same as the height t5 or may be different from theheight t5. The embossed protrusion 52 tb is structured in the same wayas the embossed protrusion 52 ta.

The wave-shaped protrusion 27 t and the embossed protrusion 52 ta are incontact with the surface 14 b of an adjacent first metal separator 14,while the inlet linear protrusion 51 ta is separated from the surface 14b. The embossed protrusion 30 ae of the first metal separator 14 is incontact with the surface 20 b of the third metal separator 20 at aposition separated farther from the inlet linear protrusion 51 ta thanthe embossed protrusion 52 ta is. The outlet linear protrusion 51 tb andthe embossed protrusion 52 tb are respectively structured in the sameway as the inlet linear protrusion 51 ta and the embossed protrusion 52ta. The embossed protrusion 30 be is structured in the same way as theembossed protrusion 30 ae.

When the surface 14 b of the first metal separator 14 adjacent to thethird metal separator 20 is placed on the surface 20 b of the thirdmetal separator 20, the coolant channel 27 is integrally formed on thesurface 20 b.

Referring to FIG. 1, a first sealing member 58 is integrally formed onthe surfaces 14 a and 14 b of the first metal separator 14 so as tosurround the outer peripheral end portion of the first metal separator14. A second sealing member 60 is integrally formed on the surfaces 18 aand 18 b of the second metal separator 18 so as to surround the outerperipheral end portion of the second metal separator 18. A third sealingmember 62 is integrally formed on the surfaces 20 a and 20 b of thethird metal separator 20 so as to surround the outer peripheral endportion of the third metal separator 20.

The first sealing member 58, the second sealing member 60, and the thirdsealing member 62 are each made of an elastic rubber material, such as asealing material, a cushioning material, or a packing material. Examplesof such materials include EPDM, NBR, fluorocarbon rubber, siliconerubber, fluorosilicone rubber, butyl rubber, natural rubber, styrenerubber, chloroprene rubber, and acrylic rubber.

Referring to FIG. 2, the first membrane electrode assembly 16 a and thesecond membrane electrode assembly 16 b each include a solid polymerelectrolyte membrane 64, which is, for example, a thin film that is madeof a perfluorosulfonic acid polymer including water. The solid polymerelectrolyte membrane 64 is sandwiched between a cathode electrode 66 andan anode electrode 68.

Each of the first membrane electrode assembly 16 a and the secondmembrane electrode assembly 16 b is a stepped MEA in which the planardimensions of the cathode electrode 66 are smaller than those of theanode electrode 68 and the solid polymer electrolyte membrane 64.Alternatively, the cathode electrode 66 may have planar dimensions thesame as those of the anode electrode 68 and the solid polymerelectrolyte membrane 64. The anode electrode 68 may have planardimensions smaller than those of the cathode electrode 66 and the solidpolymer electrolyte membrane 64.

The cathode electrode 66 and the anode electrode 68 each include a gasdiffusion layer (not shown) and an electrode catalyst layer (not shown).The gas diffusion layer is made of carbon paper or the like. Theelectrode catalyst layer is formed by uniformly coating a surface of thegas diffusion layer with porous carbon particles whose surfaces supporta platinum alloy. The electrode catalyst layers are formed, for example,on both sides of the solid polymer electrolyte membrane 64.

In the first membrane electrode assembly 16 a, a first resin framemember 70 is disposed on an outer periphery of the solid polymerelectrolyte membrane 64 so as to be located outward from an edge of thecathode electrode 66. The first resin frame member 70 is integrallyformed, for example, by injection molding. In the second membraneelectrode assembly 16 b, a second resin frame member 72 is disposed onan outer periphery of the solid polymer electrolyte membrane 64 so as tobe located outward from an edge of the cathode electrode 66. The secondresin frame member 72 is integrally formed, for example, by injectionmolding.

An electrically insulating commodity plastic, an engineering plastic, asuper engineering plastic, or the like may be used as the material ofthe first resin frame member 70 and the second resin frame member 72.Each of the resin frame members 70 and 72 may be made from, for example,a film or the like. The first resin frame member 70 and the second resinframe member 72 have outer shapes having dimensions such that the resinframe members 70 and 72 are disposed further inward than the manifolds,including the oxidant gas inlet manifold 22 a.

Referring to FIG. 1, on a surface of the first resin frame member 70 onthe cathode electrode 66 side, an inlet buffer portion 74 a is disposedbetween the oxidant gas inlet manifold 22 a and the inlet of the firstoxidant gas channel 26. On the surface of the first resin frame member70 on the cathode electrode 66 side, an outlet buffer portion 74 b isdisposed between the oxidant gas outlet manifold 22 b and the outlet ofthe first oxidant gas channel 26.

The inlet buffer portion 74 a includes a plurality of embossed portions76 a (or a flat surface), which are located close to the oxidant gasinlet manifold 22 a, and a plurality of linear inlet guide channels 78 a(or embossed portions), which are located close to the first oxidant gaschannel 26. The outlet buffer portion 74 b includes a plurality ofembossed portions 76 b (or a flat surface), which are located close tothe oxidant gas outlet manifold 22 b, and a plurality of linear outletguide channels 78 b (or embossed portions), which are located close tothe first oxidant gas channel 26.

Referring to FIG. 6, on a surface of the first resin frame member 70 onthe anode electrode 68 side, an inlet buffer portion 82 a is disposedbetween the fuel gas inlet manifold 24 a and the first fuel gas channel34. On the surface of the first resin frame member 70 on the anodeelectrode 68 side, an outlet buffer portion 82 b is disposed between thefuel gas outlet manifold 24 b and the first fuel gas channel 34.

The inlet buffer portion 82 a includes a plurality of embossed portions84 a (or a flat surface), which are located close to the fuel gas inletmanifold 24 a, and a plurality of linear inlet guide channels 86 a (orembossed portions), which are located close to the first fuel gaschannel 34. The outlet buffer portion 82 b includes a plurality ofembossed portions 84 b (or a flat surface), which are located close tothe fuel gas outlet manifold 24 b, and a plurality of linear outletguide channels 86 b (or embossed portions), which are located close tothe first fuel gas channel 34.

Referring to FIG. 1, on a surface of the second resin frame member 72 onthe cathode electrode 66 side, an inlet buffer portion 90 a is disposedbetween the oxidant gas inlet manifold 22 a and the inlet of the secondoxidant gas channel 38. On the surface of the second resin frame member72 on the cathode electrode 66 side, an outlet buffer portion 90 b isdisposed between the oxidant gas outlet manifold 22 b and the outlet ofthe second oxidant gas channel 38.

The inlet buffer portion 90 a includes a plurality of embossed portions92 a (or a flat surface), which are located close to the oxidant gasinlet manifold 22 a, and a plurality of linear inlet guide channels 94 a(or embossed portions), which are located close to the second oxidantgas channel 38. The outlet buffer portion 90 b includes a plurality ofembossed portions 92 b (or a flat surface), which are located close tothe oxidant gas outlet manifold 22 b, and a plurality of linear outletguide channels 94 b (or embossed portions), which are located close tothe second oxidant gas channel 38.

Referring to FIG. 7, on a surface of the second resin frame member 72 onthe anode electrode 68 side, an inlet buffer portion 98 a is disposedbetween the fuel gas inlet manifold 24 a and the second fuel gas channel48. On the surface of the second resin frame member 72 on the anodeelectrode 68 side, an outlet buffer portion 98 b is disposed between thefuel gas outlet manifold 24 b and the second fuel gas channel 48.

The inlet buffer portion 98 a includes a plurality of embossed portions100 a (or a flat surface), which are located close to the fuel gas inletmanifold 24 a, and a plurality of linear inlet guide channels 102 a (orembossed portions), which are located close to the second fuel gaschannel 48. The outlet buffer portion 98 b includes a plurality ofembossed portions 100 b (or a flat surface), which are located close tothe fuel gas outlet manifold 24 b, and a plurality of linear outletguide channels 102 b (or embossed portions), which are located close tothe second fuel gas channel 48.

When two power generation cells 12 are stacked on top of each other, thecoolant channel 27 is formed between the first metal separator 14 of oneof the power generation cells 12 and the third metal separator 20 of theother power generation cell 12 (see FIGS. 1 and 2).

An operation of the fuel cell 10, which is structured as describedabove, will be described.

Referring to FIG. 1, an oxidant gas, such as an oxygen-containing gas,is supplied to the oxidant gas inlet manifold 22 a. A fuel gas, such asa hydrogen-containing gas, is supplied to the fuel gas inlet manifold 24a. A coolant, such as pure water, ethylene glycol, or oil, is suppliedto the pair of coolant inlet manifolds 25 a.

A part of the oxidant gas flows through the oxidant gas inlet manifold22 a, the inlet buffer portion 74 a, and the first oxidant gas inletbuffer portion 30 a; and is supplied to the first oxidant gas channel 26of the first metal separator 14 (see FIGS. 1 to 3). The remaining partof the oxidant gas flows through the oxidant gas inlet manifold 22 a,the inlet buffer portion 90 a, and the second oxidant gas inlet bufferportion 42 a; and flows into the second oxidant gas channel 38 of thesecond metal separator 18 (see FIGS. 1 and 4).

Referring to FIGS. 1, 3, and 4, the oxidant gas is supplied to thecathode electrode 66 of the first membrane electrode assembly 16 a whileflowing along the first oxidant gas channel 26 in the direction of arrowB (horizontal direction). Likewise, the oxidant gas is supplied to thecathode electrode 66 of the second membrane electrode assembly 16 bwhile flowing along the second oxidant gas channel 38 in the directionof arrow B.

Referring to FIGS. 1 and 6, the fuel gas flows through the fuel gasinlet manifold 24 a and the inlet connection grooves 35 a of the secondmetal separator 18 and is supplied to the inlet buffer portion 82 a andthe first fuel gas inlet buffer portion 37 a. Likewise, referring toFIGS. 1 and 7, the fuel gas flows through the inlet connection grooves54 a of the third metal separator 20 and is supplied to the inlet bufferportion 98 a and the second fuel gas inlet buffer portion 53 a.Therefore, the fuel gas is supplied to the first fuel gas channel 34 ofthe second metal separator 18 and the second fuel gas channel 48 of thethird metal separator 20.

The fuel gas is supplied to the anode electrode 68 of the first membraneelectrode assembly 16 a while flowing along the first fuel gas channel34 in the direction of arrow B. Likewise, the fuel gas is supplied tothe anode electrode 68 of the second membrane electrode assembly 16 bwhile flowing along the second fuel gas channel 48 in the direction ofarrow B.

Accordingly, in the first membrane electrode assembly 16 a and thesecond membrane electrode assembly 16 b, the oxidant gas supplied to thecathode electrodes 66 and the fuel gas supplied to the anode electrodes68 cause electrochemical reactions in the electrode catalyst layers, andthereby electric power is generated.

The oxidant gas, which has been supplied to the cathode electrodes 66 ofthe first membrane electrode assembly 16 a and the second membraneelectrode assembly 16 b and partially consumed, is discharged to theoutlet buffer portions 74 b and 90 b. The oxidant gas is discharged fromthe first oxidant gas outlet buffer portion 30 b and the second oxidantgas outlet buffer portion 42 b to the oxidant gas outlet manifold 22 b.

The fuel gas, which has been supplied to the anode electrodes 68 of thefirst membrane electrode assembly 16 a and the second membrane electrodeassembly 16 b and partially consumed, is discharged to the outlet bufferportions 82 b and 98 b. The fuel gas is discharged from the first fuelgas outlet buffer portion 37 b and the second fuel gas outlet bufferportion 53 b to the fuel gas outlet manifold 24 b through the outletconnection grooves 35 b and 54 b.

Referring to FIG. 1, the coolant, which has been supplied to the pair ofupper and lower coolant inlet manifolds 25 a, is introduced into thecoolant channel 27. The coolant is suppled from the coolant inletmanifolds 25 a to the coolant channel 27, temporarily flows inward inthe direction of arrow C, then flows in the direction of arrow B, andcools the first membrane electrode assembly 16 a and the second membraneelectrode assembly 16 b. Then, the coolant flows outward in thedirection of arrow C and is discharged to the pair of coolant outletmanifolds 25 b.

In the present embodiment, the coolant channel 27 is formed between thesurface 14 b of the first metal separator 14 and the surface 20 b of thethird metal separator 20, which are adjacent to each other. Referring toFIG. 5, on the surface 20 b of the third metal separator 20, thewave-shaped channel grooves 27 a, which form a part of the coolantchannel 27, are formed between the plurality of wave-shaped protrusions27 t.

Referring to FIGS. 2 and 5, the inlet linear protrusions 51 ta, eachhaving a height smaller than that of each of the wave-shaped protrusions27 t, are formed so as to be continuous with the inlet end portions ofthe wave-shaped protrusions 27 t. Moreover, the embossed protrusions 52ta, each having a height larger than that of each of the inlet linearprotrusions 51 ta, are connected the end portions of the inlet linearprotrusions 51 ta. The embossed protrusions 52 ta are located closer tothe inlet linear protrusions 51 ta than the embossed protrusions 30 aeof the first metal separator 14 are.

The outlet linear protrusions 51 tb, each having a height smaller thanthat of each of the wave-shaped protrusions 27 t, are formed so as to becontinuous with the outlet end portions of the wave-shaped protrusions27 t. Moreover, the embossed protrusions 52 tb, each having a heightlarger than that of each of the outlet linear protrusions 51 tb, areconnected the end portions of the outlet linear protrusions 51 tb. Theembossed protrusions 52 tb are located closer to the outlet linearprotrusions 51 tb than the embossed protrusions 30 be of the first metalseparator 14 are.

Therefore, referring to FIG. 2, each of the inlet linear protrusions 51ta is separated from the surface 14 b of an adjacent first metalseparator 14, while each of the wave-shaped protrusions 27 t and theembossed protrusions 52 ta is in contact with the surface 14 b.Accordingly, a bending stress applied to the inlet linear protrusions 51ta can be effectively reduced.

Thus, in the contact portion between the first metal separator 14 andthe third metal separator 20, the distance over which the first andthird metal separators 14 and 20 are held between the protrusions can bereduced. Therefore, with a simple structure, deformation of the firstmetal separator 14 and the third metal separator 20 when a differentialpressure is applied can be effectively suppressed.

In the present embodiment, the power generation cell 12 includes threemetal separators and two MEAs. However, this is not a limitation. Forexample, the power generation cell 12 may include two metal separatorsand one MEA.

According to one aspect of the embodiment, a fuel cell includes amembrane electrode assembly in which electrodes are disposed on bothsides of an electrolyte membrane, and metal separators stacked on themembrane electrode assembly. A coolant channel is formed between a firstmetal separator and a second metal separator that are adjacent to eachother, the coolant channel allowing a coolant to flow in a directionalong an electrode surface.

The first metal separator includes wave-shaped protrusions between eachpair of which a wave-shaped channel groove is formed, each of thewave-shaped protrusions having a wave shape in plan view, thewave-shaped channel groove being included in the coolant channel. Thefirst metal separator includes linear protrusions connected to both endsof each of the wave-shaped protrusions, each of the linear protrusionshaving a height smaller than that of each of the wave-shapedprotrusions; and embossed protrusions each of which is connected to anend portion of a corresponding one of the linear protrusions, each ofthe embossed protrusions having a height larger than that of each of thelinear protrusions and being in contact with the second metal separator.

In the fuel cell, preferably, the second one of the metal separatorsincludes other embossed protrusions that are located farther from thelinear protrusions than the embossed protrusions of the first one of themetal separators are, the other embossed protrusions protruding in adirection opposite to a direction in which the embossed protrusions ofthe first one of the metal separators protrude and each having a heightthe same as that of each of the embossed protrusions of the first one ofthe metal separators.

With the present disclosure, the linear protrusions each have a heightsmaller than that of each of the wave-shaped protrusions, and theembossed protrusions, each having a height larger than that of each ofthe linear protrusions, are disposed at the end portions of the linearprotrusions. Therefore, the first one of the metal separators can be incontact with the second one of the metal separators at the wave-shapedprotrusions and the embossed protrusions. Accordingly, a bending stressapplied to the linear protrusions can be effectively reduced.

Thus, in the contact portion between the metal separators, the distanceover which the metal separators are held between the protrusions can bereduced. Therefore, with a simple structure, deformation of the metalseparators when a differential pressure is applied can be effectivelysuppressed.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. A fuel cell comprising: a membrane electrodeassembly in which electrodes are disposed on both sides of anelectrolyte membrane; and metal separators stacked on the membraneelectrode assembly, wherein a coolant channel is formed between a firstmetal separator and a second metal separator that are adjacent to eachother, the coolant channel allowing a coolant to flow in a directionalong an electrode surface, wherein the first metal separator includeswave-shaped protrusions between each pair of which a wave-shaped channelgroove is formed, each of the wave-shaped protrusions having a waveshape in plan view, the wave-shaped channel groove being included in thecoolant channel, linear protrusions connected to both ends of each ofthe wave-shaped protrusions, each of the linear protrusions having aheight smaller than that of each of the wave-shaped protrusions suchthat the linear protrusions are separated from and are not in contactwith the second metal separator, and embossed protrusions each of whichis connected to an end portion of a corresponding one of the linearprotrusions, each of the embossed protrusions having a height largerthan that of each of the linear protrusions and being in direct contactwith the second metal separator, and wherein the second metal separatorincludes other embossed protrusions that are located farther from thelinear protrusions than the embossed protrusions of the first metalseparator are, the other embossed protrusions protruding in a directionopposite to a direction in which the embossed protrusions of the firstmetal separator protrude and each having a height the same as that ofeach of the embossed protrusions of the first metal separators.
 2. Afuel cell comprising: a membrane electrode assembly having a first endand second end opposite to the first end in an extending direction andcomprising: an electrolyte membrane; and first and second electrodessandwiching the electrolyte membrane therebetween in a stackingdirection substantially perpendicular to the extending direction; afirst metal separator stacked on the membrane electrode assembly in thestacking direction; a second metal separator stacked on the first metalseparator in the stacking direction to define a coolant channel betweenthe first metal separator and the second metal separator, the coolantchannel extending in the extending direction; the first metal separatorincluding wave-shaped protrusions each of which has a wave shape viewedin the stacking direction and projects from the first metal separatortoward the second metal separator by a first height in the stackingdirection to define a wave-shaped channel groove between the wave-shapedprotrusions to form the coolant channel, each of the wave-shapedprotrusions having a first distal end and a second distal end oppositeto the first distal end in the extending direction; first and secondlinear protrusions connected to the first distal end and the seconddistal end of each of the wave-shaped protrusions, respectively, each ofthe first and second linear protrusions having a straight shapeextending in the extending direction and projecting from the first metalseparator toward the second metal separator by a second height in thestacking direction, the second height being smaller than the firstheight, the first and second linear protrusions being separated from andnot in contact with the second metal separator; and first and secondembossed protrusions connected to a first tip end of the first linearprotrusion and a second tip end of the second linear protrusion,respectively, the first and second embossed protrusions projecting fromthe first metal separator toward the second metal separator by a thirdheight in the stacking direction to be in direct contact with the secondmetal separator, the third height being larger than the second height,wherein the second metal separator includes other embossed protrusionsthat are located farther from the linear protrusions than the embossedprotrusions of the first metal separator are, the other embossedprotrusions protruding in a direction opposite to a direction in whichthe embossed protrusions of the first metal separator protrude and eachhaving a height the same as that of each of the embossed protrusions ofthe first metal separators.
 3. The fuel cell according to claim 2,wherein the first and second embossed protrusions are directly connectedto the first linear protrusion and the second linear protrusion,respectively.
 4. The fuel cell according to claim 1, wherein theembossed protrusions project toward the second metal separator.
 5. Thefuel cell according to claim 1, wherein the embossed protrusions aredirectly connected to the corresponding one of the linear protrusions.6. A fuel cell comprising: a membrane electrode assembly in whichelectrodes are disposed on both sides of an electrolyte membrane; andmetal separators stacked on the membrane electrode assembly, wherein acoolant channel is formed between a first metal separator and a secondmetal separator that are adjacent to each other, the coolant channelallowing a coolant to flow in a direction along an electrode surface,wherein the first metal separator includes wave-shaped protrusionsbetween each pair of which a wave-shaped channel groove is formed, eachof the wave-shaped protrusions having a wave shape in plan view, thewave-shaped channel groove being included in the coolant channel, linearprotrusions connected to both ends of each of the wave-shapedprotrusions, each of the linear protrusions having a height smaller thanthat of each of the wave-shaped protrusions such that the linearprotrusions are separated from and are not in contact with the secondmetal separator, and embossed protrusions each of which is connected toan end portion of a corresponding one of the linear protrusions, each ofthe embossed protrusions having a height larger than that of each of thelinear protrusions and being in direct contact with the second metalseparator, wherein the first metal separator has a longitudinaldirection, and wherein both ends of each of the wave-shaped protrusionsare substantially aligned in the longitudinal direction.
 7. The fuelcell according to claim 6, wherein the wave-shaped protrusions each havea shape extending along the longitudinal direction with a waveperiodically provided along a second direction perpendicular to thelongitudinal direction.
 8. A fuel cell comprising: a membrane electrodeassembly having a first end and second end opposite to the first end inan extending direction and comprising: an electrolyte membrane; andfirst and second electrodes sandwiching the electrolyte membranetherebetween in a stacking direction substantially perpendicular to theextending direction; a first metal separator stacked on the membraneelectrode assembly in the stacking direction; a second metal separatorstacked on the first metal separator in the stacking direction to definea coolant channel between the first metal separator and the second metalseparator, the coolant channel extending in the extending direction; thefirst metal separator including wave-shaped protrusions each of whichhas a wave shape viewed in the stacking direction and projects from thefirst metal separator toward the second metal separator by a firstheight in the stacking direction to define a wave-shaped channel groovebetween the wave-shaped protrusions to form the coolant channel, each ofthe wave-shaped protrusions having a first distal end and a seconddistal end opposite to the first distal end in the extending direction;first and second linear protrusions connected to the first distal endand the second distal end of each of the wave-shaped protrusions,respectively, each of the first and second linear protrusions having astraight shape extending in the extending direction and projecting fromthe first metal separator toward the second metal separator by a secondheight in the stacking direction, the second height being smaller thanthe first height, the first and second linear protrusions beingseparated from and not in contact with the second metal separator; andfirst and second embossed protrusions connected to a first tip end ofthe first linear protrusion and a second tip end of the second linearprotrusion, respectively, the first and second embossed protrusionsprojecting from the first metal separator toward the second metalseparator by a third height in the stacking direction to be in directcontact with the second metal separator, the third height being largerthan the second height, wherein the first distal end substantiallyaligns with the second distal end in the extending direction.
 9. Thefuel cell according to claim 8, wherein the wave-shaped protrusions eachhave a shape extending along the extending direction with a waveperiodically provided along a second direction perpendicular to theextending direction.